Caffeine is the most widely used psychoactive drug in the world. Its effects on behavior and neurotransmitter levels are similar to those of cocaine and other psychomotor stimulants, yet its status as a drug of abuse is controversial. Caffeine also has the unique status in this country of being the only legal, nonprescription psychoactive drug that children may purchase and consume in unrestricted quantities. The overall goal of the proposed research is to study the effects of caffeine and caffeine withdrawal on learning and performance in adolescent and adult monkeys, because little is known about the consequences of caffeine use -on learning and performance in developing organisms. In addition, interactions between caffeine and cocaine will be examined with respect to reinforcing and withdrawal effects. Although caffeine is a drug that can be examined in human subjects, the use of monkeys allows for parametric manipulations and multiple within-subject comparisons that are not easily accomplished in human subjects. The specific aims of this project are: 1) To determine whether caffeine differentially affects learning and performance, 2) To examine the effects of caffeine withdrawal on learning and performance, 3) To assess the reinforcing effects of caffeine by comparing selection of caffeinated and noncaffeinated beverages, 4) To evaluate the effects of caffeine exposure on self-administration of smoked cocaine base (both of these procedures have been well established), and 5) To compare the effects of combined caffeine and cocaine withdrawal to withdrawal of each drug alone. Experiments will be conducted with 10 male rhesus monkeys; 5 will be adolescents and 5 will be adults. The age groups will be separated by approximately 5 years. The monkeys will be trained to self-administer orally delivered caffeine via lip-operated solenoid-driven drinking devices, and cocaine will be self-administered by smoking cocaine base. These experiments will determine whether caffeine and caffeine withdrawal differentially affect learning and performance in adolescent and adult monkeys, and they will evaluate the addictive effects of caffeine and its interaction with cocaine self-administration.